20 research outputs found
An adaptive inelastic magnetic mirror for Bose-Einstein condensates
We report the reflection and focussing of a Bose-Einstein condensate by a new
pulsed magnetic mirror. The mirror is adaptive, inelastic, and of extremely
high optical quality. The deviations from specularity are less than 0.5 mrad
rms, making this the best atomic mirror demonstrated to date. We have also used
the mirror to realize the analog of a beam-expander, producing an ultra-cold
collimated fountain of matter wavesComment: 4 pages, 4 figure
A quantum mechanical description of the experiment on the observation of gravitationally bound states
Quantum states in the Earth's gravitational field were observed, when
ultra-cold neutrons fall under gravity. The experimental results can be
described by the quantum mechanical scattering model as it is presented here.
We also discuss other geometries of the experimental setup which correspond to
the absence or the reversion of gravity. Since our quantum mechanical model
describes, particularly, the experimentally realized situation of reversed
gravity quantitatively, we can practically rule out alternative explanations of
the quantum states in terms of pure confinement effects.Comment: LaTeX, 10 pages, 4 figures, v2: references adde
Fractional quantum revivals in the atomic gravitational cavity
In this paper we discuss the quantum dynamics and fractional quantum revivals of an integrable nonlinear system, consisting of an atom bouncing vertically from an evanescent field, for two cases with the simplified infinite-potential and the more practical exponential potential, respectively. We study the two cases separately, then contrast and compare the results and reach the conclusion that provided the starting position of the atoms is not too close to the reflecting surface supporting the evanescent wave (this condition is always satisfied in present experiments in this field), the two cases will produce the same results. This means that the idealized infinite potential is a good approximation to the more realistic exponential potential. Because the quantum analysis of the infinite-potential case is quite simple and straighforward (since its Schrödinger equation has analytical solutions), this will greatly simplify the quantum analysis of the more complicated exponential potential case and hence has practical significance
Deconstructing Decoherence
The study of environmentally induced superselection and of the process of
decoherence was originally motivated by the search for the emergence of
classical behavior out of the quantum substrate, in the macroscopic limit. This
limit, and other simplifying assumptions, have allowed the derivation of
several simple results characterizing the onset of environmentally induced
superselection; but these results are increasingly often regarded as a complete
phenomenological characterization of decoherence in any regime. This is not
necessarily the case: The examples presented in this paper counteract this
impression by violating several of the simple ``rules of thumb''. This is
relevant because decoherence is now beginning to be tested experimentally, and
one may anticipate that, in at least some of the proposed applications (e.g.,
quantum computers), only the basic principle of ``monitoring by the
environment'' will survive. The phenomenology of decoherence may turn out to be
significantly different.Comment: 13 two-column pages, 3 embedded figure
Creating a low-dimensional quantum gas using dark states in an inelastic evanescent-wave mirror
We discuss an experimental scheme to create a low-dimensional gas of
ultracold atoms, based on inelastic bouncing on an evanescent-wave mirror.
Close to the turning point of the mirror, the atoms are transferred into an
optical dipole trap. This scheme can compress the phase-space density and can
ultimately yield an optically-driven atom laser. An important issue is the
suppression of photon scattering due to ``cross-talk'' between the mirror
potential and the trapping potential. We propose that for alkali atoms the
photon scattering rate can be suppressed by several orders of magnitude if the
atoms are decoupled from the evanescent-wave light. We discuss how such dark
states can be achieved by making use of circularly-polarized evanescent waves.Comment: 8 pages, 4 figure
Cold atom dynamics in non-Abelian gauge fields
The dynamics of ultracold neutral atoms subject to a non-Abelian gauge field
is investigated. In particular we analyze in detail a simple experimental
scheme to achieve a constant, but non-Abelian gauge field, and discuss in the
frame of this gauge field the non-Abelian Aharanov-Bohm effect. In the last
part of this paper, we discuss intrinsic non-Abelian effects in the dynamics of
cold atomic wavepackets.Comment: 8 pages, 9 figure
Numerical Modeling of Evanescent-Wave Atom Optics
We numerically solve the time-dependent Schrodinger equation for a two-level atom interacting with an evanescent light field. The atom may be reflected or diffracted. Using the experimental parameter values we quantitatively model the evanescent field dopplerons (velocity-tuned resonances) observed by Stenlake et al. [Phys. Rev. A 49, 16 (1994)]. Besides successfully modeling the experiment, our approach provides complementary insights to the usual solution of the time-independent Schrodinger equation. We neglect spontaneous emission
Matter-wave cavity gravimeter
We propose a gravimeter based on a matter-wave resonant cavity loaded with a
Bose-Einstein condensate and closed with a sequence of periodic Raman pulses.
The gravimeter sensitivity increases quickly with the number of cycles
experienced by the condensate inside the cavity. The matter wave is refocused
thanks to a spherical wave-front of the Raman pulses. This provides a
transverse confinement of the condensate which is discussed in terms of a
stability analysis. We develop the analogy of this device with a resonator in
momentum space for matter waves.Comment: 15 pages, 6 Figures. The expression for the atomic mirror focal
length has been corrected. Other minor corrections and actualizations to the
previously published versio
Velocity-selective optical pumping and collision effects
Optical pumping performed with a quasi monochromatic laser beam in an atomic gas introduces a redistribution of Zeeman populations selectively in a single velocity class. In the limit of low pumping intensity the rate theory is valid for a description of velocity-selective optical pumping (V.S.O.P.). Well-defined atomic observables (population, orientation, alignment) and their velocity-correlated collisional relaxation can be studied. Also, a modified scheme for the detection of second order effects of optical pumping allows one to observe light shift induced signals. In particular, V.S.O.P. and its combination with modulated pumping, magnetic depolarization (level crossing), and magnetic resonance techniques provide information about the atomic collision characteristics such as collision rates and kernels for velocity-changing collisions
Effet de déplacements lumineux dans une expérience de pompage optique sélectif en vitesses
An effect of light-shifts has been observed in a velocity-selective optical pumping experiment ; this effect couples two alignments to produce an orientation. A Doppler-free dispersion-shaped signal is obtained when the laser frequency is tuned over the atomic resonance. The experimental geometry allows here to observe this effect with a very good signal-to-noise ratio.Nous avons observé, dans une expérience de pompage optique sélectif en vitesses, un effet de déplacements lumineux qui couple deux alignements pour produire une orientation. Cet effet donne lieu, quand on balaie la fréquence du laser, à un signal de dispersion sans effet Doppler. La géométrie expérimentale utilisée ici permet d'observer cet effet avec un excellent rapport signal sur bruit